1. Field of the Invention
Embodiments of the present invention generally relate to wireless devices and more specifically to receiving and transmitting signals between transceivers.
2. Description of the Related Art
Generally, a communication system includes a transmitter and receiver which transmit and receive information signals over a transmission media such as wires or atmosphere. When atmosphere is used, the transmission is commonly referred to as “wireless communication”. Examples of various types of wireless communication systems include digital cellular, packet data paging, wireless local area networks (LAN), wireless wide area networks (WAN), personal communication systems, and others.
One problematic issue relates to increasing wireless network capacity. As more users are added to a wireless network, the more information each wireless network transceiver (card) is required to handle. Others have attempted to solve this issue by using a plurality of wireless network cards to increase wireless system capacity. To minimize floor space usage, often the plurality of wireless network cards are placed in a “rack” system, often in close proximity to one another. This methodology also allows the sharing of electrical power and communication busses between the various wireless network cards for common control thereof. Unfortunately, transmitters and receivers of the wireless network cards placed in proximity to one another can cause cross talk and interference issues. For example, consider the case of co-located devices where a transmitter A is positioned in proximity to a receiver B, and transmitter A and receiver B are operating at approximately the same radio frequency (RF). Due to the spatial proximity between transmitter A to receiver B, when transmitter A is transmitting a RF signal to another receiver C, the output power of transmitter A may overload the input of receiver B, especially if receiver B has increased its input sensitivity to receive a weak signal from a distant transmitter (D).
As just described, this problem is particularly serious when one wireless network card is transmitting while another is receiving. Some wireless networking systems employ protocols that can be configured to avoid this situation. For example, Time Division Multiple Access (TDMA) systems allow the base station to control when each device transmits or receives. In this way, co-located devices could be scheduled such that one does not transmit while the other is receiving. Code Division Multiple Access (CDMA) systems have coding gain. By assigning different codes to the co-located devices, the damage that occurs when one transmits while another is receiving can be minimized. Finally, some wireless communication systems are based on polling, which like TDMA allows the transmissions of each device to be controlled by a centralized controller which transmits the polls allowing individual devices to transmit. By proper timing of the polling, the case of one co-located device transmitting while another is receiving can be avoided.
Others have tried to correct the problem of uncoordinated transmission times, where a co-located device transmits while another receives, by using wireless network cards having narrow RF filters that limit each card to specific frequencies of operation. Unfortunately, this methodology may require procuring and maintaining a stock of different wireless network cards for each narrow frequency sub-range. Still others have tried to use spatially separated antennas or used directional antenna systems. Some have used time sharing solutions where only one wireless card is allowed to communicate at a time. All of the above solutions generally add complexity, reduce flexibility or performance, and increase the overall cost of the wireless network.